From Colin McDonald and Robert Osfield, "When a serializer shared library is loaded it registers all of
the wrappers it contains.  The registration creates a prototype
object for all of the wrapped classes.  For some of the higher-level
classes this can be a bit heavy.

I noticed a problem with a model which required a single class from
osgSim.  When osgdb_serializers_osgsim.so was loaded it registered
wrappers and created prototype objects for all of the osgSim classes,
including osgSim::ScalarBar.  The constructor for that class creates
several drawables, and loads arial.ttf using the freetype plugin.  I
don't need that, and don't even ship the font or plugin with my
application, resulting in an unexplained warning message loading
the model.

I've modified the ObjectWrapper class to defer the prototype object
creation until if & when actually required."